Not only is the Reverse Flash causing all kinds of problems with the time stream and killing off Justice Society characters(!), but both Dr. Stein and Jefferson discover Rip Hunter's secret compartment on board the Waverider that contains a secret message from The Flash/Barry Allen from the future year 2056.

In Barry's message to Rip Hunter, The Flash tells Rip that a war is coming!

"I can't risk putting anymore lives in danger, and neither can you," the future Flash says, voiced by Grant Gustin, in the message meant only for Rip Hunter. "Which is why you will keep what I'm about to tell you a secret. Even from the rest of your team. A war is coming Captain Hunter."

Jefferson turns off the future Flash's message after that, which may mean subsequent episodes will reveal further details.

While it's unknown what war the future Flash is referring to, it could be the upcoming crossover between The Flash, Legends, Arrow and Supergirl that sees the alien race known as the Dominators come to Earth in search of metahumans (known as Invasion! in the comics).

Another possibility is that in the Young Justice TV series, the year 2056 is from when Barry Allen's grandchild, Bart Allen, travels back in time to join Young Justice and save his grandfather, The Flash, and the future. Could we see Bart Allen on The Flash? The series does feature a heck of a lot of speedsters, so it can't be ruled out.

The first season of The Flash also teased a newspaper from the future, which was from the year 2024, and interestingly enough was discovered in its own hidden compartment located within Star Labs.